We propose to use our established and well documented history in the development of biomaterials as scaffolding for tissue replacement as a platform for stem cell approaches in craniofacial tissue regeneration. The governing hypotheses of this work include: i) that human stem cells of embryonic origin can be differentiated into craniofacial tissue producing cells such as osteoblasts and chondrocytes, ii) that highthroughput techniques can be used for the screening of large numbers of media and polymer candidates for potential use with tissue engineering scaffolds, and iii) that the appropriate combination of stem cells with 3-dimensional polymer scaffolds can be used for the production of complex craniofacial tissues. To test these hypotheses, we propose the following: Aim 1: Examine the in vitro differentiation of human embryonic stem cells into precursors of craniofacial tissues. Our previous work investigating the in vitro differentiation of human embryonic stem cells into various cell types and tissues will be continued to assess conditions necessary for differentiation into cell types necessary for craniofacial tissue formation. Aim 2: Investigate the interaction of human stem cells with polymer surfaces using high-throughput screening technology. Recently, we have developed techniques for the rapid screening of cell/polymer interactions using nanoliter-scale microarrays of various monomers and polymers. Success will be assessed through cell proliferation and the presence of tissue specific markers for craniofacial tissues. Aim 3: Assess in vitro tissue production by differentiated and undifferentiated human embryonic stem cell seeded polymeric scaffolds incorporating various genes and growth factors. Polymeric materials that support the differentiation of human stem cells into craniofacial tissues will be fabricated into 3-dimensional scaffolds incorporating various genes and growth factors and analyzed by histological staining of various markers. Aim 4: Optimal candidates from the previous aims will be seeded with differentiated and undifferentiated cells and implanted either subcutaneously or in a critical sized defect model in rats. The subcutaneous model in athymic rats will be used to assess tissue production by stem cell seeded scaffolds in an in vivo environment, including scaffolds with cells differentiated into multiple phenotypes. The cranial defect model in athymic rats is a clinically relevant model that is commonly used as a measure of bone regeneration.